1. Field of the Invention
The present invention relates to polymeric blends based on vinyl-aromatic polymers, and more particularly to blends which contain an alkenyl-aromatic resin and are suitable to be transformed into shaped articles by injection moulding extrusion or other known processing techniques for thermoplastic polymers.
2. Description of the Prior Art
From British Patent Application No. 2,067,579A are known vinyl-aromatic polymers which possess an improved stress cracking resistance and are particularly suitable to be moulded or cavuum shaped.
These vinyl-aromatic polymers modified with rubber are characterized in that they contain from 6 to 12% by weight of an ethylenically unsaturated nitrile, such as acrylonitrile, bound to the two phase system of the polymer, and exhibit the following particular combination of characteristics:
(a) the dispersed elastomeric gel phase insoluble in toluene is not less than 23% by weight; PA1 (b) the swelling index of the elastomeric phase in toluene is greater than 10; PA1 (c) the melt index of the polymer is at least 1.5 g./10 min,; PA1 (d) the bending modulus of the polymer is greater than 15,000 kg/cm.sup.2 ; PA1 (e) the torsional modulus of the polymer is greater than 5,500 kg/cm.sup.2 ; PA1 (f) the notched IZOD impact strength at 23.degree. C. of the polymer is greater than 7 kg. cm/cm. PA1 (a) an aromatic polycarbonate having repeating structural units of the formula: ##STR1## in which R.sub.1, R.sub.2, R.sub.3 and R.sub.4 each represents hydrogen or an alkyl radical containing from 1 to 3 carbon atoms, and A represents --0--, --CO--, --SO.sub.2 --, an alkylene radical containing from 1 to 10 carbon atoms, an alkylidene radical containing from 1 to 10 carbon atoms, a cyclo-alkylene radical containing from 5 to 15 carbon atoms, a cyclo-alkylidene radical containing from 5 to 15 carbon atoms or the radical: ##STR2## and (b) a crystalline aromatic polyester obtained by polymerization of a glycol of general formula: EQU HO--(CH.sub.2).sub.n --OH (II) PA1 in which n is an integer from 2 to 10, with a bicarboxylic acid of formula: EQU HOOC--R.sub.5 --B--R.sub.6 --COOH (III) PA1 in which R.sub.5 and R.sub.6 each represents --(CH.sub.2).sub.m where m is zero or an integer from 1 to 4 and B is a bivalent aromatic radical represented by: ##STR3## in which D may be: --(CH.sub.2).sub.p --; --(CH.sub.2).sub.p --CO--(CH.sub.2).sub.p --; --(CH.sub.2).sub.p --O--(CH.sub.2).sub.p --; --O--(CH.sub.2).sub.q --O--; ##STR4## where p may be zero or an integer from 1 to 5 and q is an integer from 1 to 5.
The methods of measuring the above-mentioned characteristics are described in the Patent Application No. 2 067 579A.
Such modified vinyl-aromatic polymers are particularly suitable to be used in the production both of refrigerator cells and of other articles obtained by thermoforming the extruded sheets. Such polymers can be easily manufactured by processes which are presently in use. Furthermore, they are compatible both with polystyrol or impact resistant polystyrol, as wel as with ABS thermopolymers and styrol/acrylonitrile copolymers (SAN).
Nevertheless, these vinyl-aromatic polymers modified with an ethylenically unsaturated nitrile, and also in general all vinyl-aromatic polymers, have the drawback of having a low heat distorsion temperature so that their thermal resistance is not sufficiently satisfactory to meet the necessary requirements in some fields of application, for example in the automotive industry.